Backpacks, or knapsacks, are essentially pliable, durable bags or cases equipped with shoulder straps that allow the backpack to be worn on the back for carrying equipment, supplies, or other small articles. Backpacks are frequently used for sporting endeavors such as hiking, skating, skiing, hunting, and biking. Backpacks are also commonly used to carry electronic equipment such as radios or computers. A relatively new application for backpacks is the hydration pack, which is designed to carry a fluid, such as water, and typically includes a valve and tube leading from the fluid container to the user, that allows the user to drink while wearing the backpack on his or her back without interrupting whatever activity in which the user is engaged. The hydration pack may include additional compartments to accommodate non-fluid articles.
Because conventional backpacks are carried adjacent the user's back, thereby limiting or completely eliminating air flow thereto, the user's back is prevented or hindered from normal cooling. The backpack can become uncomfortable when worn for an extended period of time, especially if the user is engaged in a strenuous physical activity. In particular, the user's clothing, the backpack, and even the contents of the backpack, can rapidly become saturated with sweat, which does not readily evaporate under the pack. During strenuous activities, the inability of the user to efficiently discard heat may also undesirably limit the duration of the user's activities or even contribute to heat-related ailments such as dehydration or sun stroke. Ironically, when the user is engaged in strenuous activities such as bicycling, skiing, and skating (and to a lesser extent activities such as hiking), the user is generally moving rapidly with respect to the surrounding air, and therefore experiencing significant convective and evaporative cooling over some portion of the user's body. Conventional backpacks, however, block the user's back from the air flow, and prevent the back from such convective and evaporative cooling.
It may also be difficult to keep items in the backpack cool when that is desired, for example, when the backpack is a hydration pack. Significant heat may transfer to the backpack due to the close contact between the backpack and the user.